This invention relates to Mycobacterium tuberculosis, other bacterial pathogens whose antigenicity is not caused by a single protein or component, and parasites, including detection thereof, diagnosis of infection and disease, and preparation of vaccines:
One of the important goals of research on Mycobacterium tuberculosis, the causative agent of tuberculosis (TB), is the identification of mycobacterial antigens that induce protective T-cell responses and/or stimulate humoral immunity during tubercular infection. Antigens in the former class constitute potential candidates for the development of effective vaccines, while those in the latter group can be tested as new, improved tools for diagnosis of TB.
Similarly, numerous other bacterial pathogens have pathogenicity that, as with TB, is not caused by a single protein, as is the case also with parasites generally. Antigens produced by these pathogens are also potential candidates for the development of effective vaccines.
Proteins that are actively secreted by M. tuberculosis have attracted considerable attention as potent immunogens. The observation that only live, dividing mycobacteria efficiently induce protective immunity (7, 22) led to the hypothesis that proteins that are actively secreted by M. tuberculosis during growth are key in generating protective T-cell responses (4, 23). Indeed, experimental vaccines based on culture filtrate proteins have been shown to induce some levels of protective immunity in animal models of. TB (5, 14, 15, 26). Secreted proteins of M. tuberculosis are also potent inducers of antibody production (13).
The identification and immunochemical characterization of individual components of M. tuberculosis culture filtrates is a crucial step toward understanding the role of the secreted proteins in inducing immune responses during the course of TB. More than 30 proteins are present in filtrates from short-term (4-5 day) cultures (3), prior to any substantial contamination of the filtrates by intracellular components released by autolysis of aging cells. Only about ten actively secreted proteins have been identified using antibodies from immunized animals (1); most of them have been characterized by gene cloning and nucleotide sequencing (2, 6, 9, 11, 17-20, 29, 34). Some of the known secreted proteins induce cellular immune responses (35); however, strong human T-cell responses to secreted protein fractions involve yet uncharacterized antigens in the cell filtrate (8, 29).
An aspect of this invention is an isolated DNA sequence encoding the amino acid sequence of the MPT63 antigen, a protein secreted by M. tuberculosis, that is specific for mycobacterial species that belong to the M. tuberculosis complex, as well as recombinant polypeptide sequences encoded by that DNA.
Another aspect of this invention is an isolated DNA sequence encoding the amino acid sequence of the MTC28 antigen, another protein secreted by M. tuberculosis that is similarly specific, as well as purified natural and/or recombinant polypeptide sequences encoded by that DNA.
Another aspect of this invention is a xe2x80x9ccocktailxe2x80x9d of purified natural and recombinant protein antigens or polypeptides for immunodiagnostics or vaccines, as well as DNA cocktails for vaccines.
Other aspects of this invention are in vitro and in vivo methods of detection of immune responses using the protein or polypeptide cocktails and DNA cocktails of this invention.
The gene for the protein MPT63 has been isolated and sequenced (SEQ ID NO:1). That gene can be incorporated into a plasmid and expressed in E. coli to produce purified MPT63 protein, whose sequence (SEQ ID NO:2) has been deduced. Additional expression systems will be apparent to persons skilled in the art.
The gene for the protein MTC28 has been isolated and sequenced (SEQ ID NO:3). That gene can be similarly expressed to produce purified MTC28 protein, whose sequence (SEQ ID NO:4) has been deduced.
Both MPT63 and MTC28 are proteins secreted by M. tuberculosis. Both are specific to the M. tuberculosis complex, which includes M. tuberculosis, M. bovis, M. microti, and M. africanum. 
This invention includes the MPT63 amino acid sequence shown in FIG. 1 (SEQ ID NO:2) and the MTC28 amino acid sequence shown in FIG. 2 (SEQ ID NO:3). A preferred embodiment is the mature recombinant MPT63 protein which is the polypeptide extending from the A in the underlined AYPIT to the C-terminal P in FIG. 1, and the mature recombinant MTC28 protein which extends from the D following the underlined portion to the C-terminal R in FIG. 2. Also preferred are antigenic polypeptides derived from the sequences shown in FIG. 1 and FIG. 2, whether produced by natural, recombinant or synthetic (including chemical synthesis) means or other means known in the art. The invention also includes variants of these polypeptides that retain their antigenic and immunogenic properties.
This invention also includes vaccines that contain a recombinant MPT63 polypeptide or a recombinant MTC28 polypeptide. In preferred embodiments the vaccine includes either mature recombinant protein.
This invention includes a method of eliciting an immune response and/or protective immunity against M. tuberculosis or another member of the M. tuberculosis complex in a vertebrate, said method including administering to the vertebrate a recombinant MPT63 or MTC28 polypeptide, whereby said polypeptide elicits immune responses against the Mycobacterium in the vertebrate.
This invention includes an isolated nucleic acid having the sequence shown in FIG. 1 (SEQ ID NO:1) or FIG. 2 (SEQ ID NO:3). Other embodiments can be derived by making silent substitutions, those that do not change the amino acid sequence encoded by the nucleic acid, in the nucleic acid sequence. In preferred embodiments these nucleic acids are made by modifying the sequence by mutagenesis, recombination or synthetic (including chemical synthesis) means or other means known in the art. Also preferred are embodiments wherein the nucleic acid does not contain the entire nucleic acid sequence shown in FIG. 1 (SEQ ID NO:2) or FIG. 2 (SEQ ID NO:3), with or without silent substitutions.
A DNA vaccine according to this invention includes a vector, preferably a plasmid vector, and one or more isolated nucleotide sequences each encoding the MPT63, MTC28 polypeptide, and transcriptional and translational regulatory sequences operably linked to the isolated nucleotide sequences for expression in a cell of a vertebrate. The DNA vaccine may include the regulatory sequences of CMV immediate-early promoter and/or intron A, or other non-retroviral sequences.
This invention also includes methods of eliciting an immune response and/or protective immunity by administering to a vertebrate such a DNA vaccine, whereby expression of said nucleotide sequences in said cell elicits immune responses against the Mycobacterium.
In preferred methods of this invention the vertebrate is a human. A DNA vaccine according to this invention may be administered to a vertebrate through a route of administration selected from the group consisting of inhalation, intravenous, intramuscular, intraperitoneal, intradermal, and subcutaneous. A preferred embodiment is a method wherein the DNA vaccine is administered by contacting the DNA vaccine with a mucosal surface of the vertebrate. A preferred embodiment is a method wherein the DNA vaccine is microsphere encapsulated, and is administered by contacting the microsphere-encapsulated DNA vaccine with a mucosal surface of the vertebrate. A preferred embodiment is a method wherein the DNA vaccine is coated onto gold beads for administration to the vertebrate by particle bombardment delivery. A preferred embodiment is a method wherein the gold beads are approximately 1 pm to 2 pm in diameter. A preferred embodiment is a method wherein the protective immunity is homologous, homotypic, heterotypic, or heterologous.
This invention includes the use of mature MPT63 or MTC28 polypeptide or a fragment(s) thereof in diagnostic tests for the detection in a patient of an immune response to M. tuberculosis or another member of the M. tuberculosis complex. A diagnostic test can be performed in the format of the commonly used Mantoux or Tine test for the detection of an immune reaction in the skin. This invention also includes the use of mature MPT63 or MTC28 polypeptide, or a fragment(s) thereof, to bind antibody in human or animal sera in an ELISA, or any other solid-phase immunoassay. Several formats of solid-phase immunoassays are known in the art and can be adapted for use in this invention.
This invention includes the use of a nucleic acid sequence of this invention, as a probe for the detection of the M. tuberculosis complex. Nucleic acid detection assays are well known to those skilled in the art. Assays can involve direct or indirect detection of the target sequence. Amplification of the target sequence can also be performed prior to or as a part of detection.
Amplification can be performed with, ligase chain reaction, polymerase chain reaction, self-sustained sequence reaction, NASBA and Q-beta amplification. Specific primers for the amplification of the mpt63 gene or the mtc28 gene can be derived from the nucleic acid of the present invention by standard procedures (and tests for specificity). Such primers can be selected simply by testing 15 to 50 nucleotide long sequences derived from the gene for specific hybridization to and specific amplification of the gene in the presence of various nucleic acids expected to be present in a sample.
This invention includes mixtures of antigens, or antigen xe2x80x9ccocktailsxe2x80x9d, that include at least three and as many as six or even more M. tuberculosis antigens and/or peptides thereof, at least two of which and preferably all of which are specific to the M. tuberculosis complex. The mixture should preferably include at least two purified proteins or polypeptides that are highly immunologically active in an antibody system or in T-cell recognition, for use in serodiagnosis and skin tests, respectively.
Similar cocktails can be made of protein or polypeptide antigens expressed by other bacterial pathogens, such as Listeria, Shigella and Salmonella, or by parasites, such as Plasmodium, Leishmania and Trypanosoma.
This invention also includes vaccines, both protein-based and DNA-based. The vaccines may comprise cocktails of purified proteins or polypeptide antigens, of M. tuberculosis or another bacterial pathogen or a parasite. The vaccines may comprise cocktails of DNAs encoding such antigens. Each member of the cocktail must induce a protective immune response. For vaccines, specificity to the pathogen is not required. Preferably, the cocktail comprises the most protective antigens available.
Applications of the idea of antigen combinations for immunodiagnostics and vaccines include serodiagnosis by detection of a) specific antibodies in serum and/or in other body fluids against combinations of appropriate antigens; b) antibodies of different isotypes (IgM, IgG, IgA) combined in one test system, and specific to one antigen or to an antigen combination; c) specific antibodies and/or relevant antigen(s) present in immune complexes after immune complex dissociation, and d) free, pathogen-derived antigen(s). Free or immune complex-released antigens can be identified by using (a combination of) monoclonal antibodies. Applications also include delayed-type-hypersensitivity-based immunodiagnosis by measuring specific skin test reactivity and/or in vitro T cell proliferative responses (or cytokine production) using a mixture of purified proteins specific to the pathogen.